Carl Woese

Carl Woese was an American microbiologist who fundamentally reshaped the understanding of the deepest branches of the tree of life. Beginning in the 1970s, Woese used comparisons of the sequence of a specific ribosomal RNA molecule, present in the cells of all known organisms and central to how cells build proteins, as a kind of molecular clock to measure how distantly related different organisms are, an approach that did not depend on comparing outward physical appearance or structure the way earlier classification schemes had. This method led Woese to the discovery, announced in 1977 with collaborator Ralph Wolfe, that a group of microorganisms until then classified as unusual bacteria were in fact so genetically distinct from true bacteria that they represented an entirely separate, previously unrecognized primary domain of life, which Woese named the Archaea. This finding led Woese to propose a new three-domain system of classifying all life, Bacteria, Archaea and Eukarya, replacing or supplementing older classification schemes, a proposal that met considerable early resistance from other biologists but was eventually broadly accepted as molecular evidence accumulated. Woese spent most of his career at the University of Illinois at Urbana-Champaign and continued to develop his ideas about the deep evolutionary history of cellular life throughout his career.